The invention relates to a camshaft having a decompression device for an internal combustion engine.
In the past, the predecessor of the camshaft with a decompression device was the decompression lever. The decompression lever actuates, in particular in the case of single-cylinder two-stroke internal combustion engines, a so-called separate decompression valve in the cylinder head or, in the case of four-stroke internal combustion engines, opens one or more exhaust valves in order to reduce the cylinder interior pressure for easier starting. In this case, it is also described as a valve lifter lever. During the starting of the internal combustion engine, the decompression valve allows a part of the gas to escape from the cylinder. Because of this, the force required for cranking the internal combustion engine during starting is significantly reduced. Such decompression devices are employed mainly in single-cylinder internal combustion engines of older motor vehicles, in particular of motorcycles, mopeds, and occasionally also in smaller automobiles or tractors with single-cylinder diesel-operated internal combustion engines.
Accordingly, an automatic decompression device for internal combustion engines is known from the German publication DE 42 21 394 A1. This is a decompression device with a flyweight revolving with the camshaft of the internal combustion engine. In the position pivoted back in the stationary state and at low camshaft rotational speeds, it has a tappet lifting element protruding in the region of the cam running surface of a valve tappet and shifting the same in the valve opening direction, which through the flyweight which swings outward with rising rotational speeds is guided into a position in which it is set out of engagement with the cam running surface of the tappet.
Furthermore, an automatic decompression device for an internal combustion engine, in particular a single-cylinder diesel engine, with at least one exhaust valve and one inlet valve, which are driven by a camshaft with at least one cam, is known from German publication DE 196 36 811 A1, wherein for reducing the cranking resistance during the starting of the internal combustion engine the exhaust valve is lifted. The automatic decompression device for lifting the exhaust valve below a switching speed for the switching from decompression to compression comprises a fully automatic lifting device engaging in the cam of the exhaust valve, which brings about the exhaust valve being lifted off the valve seat.
A further generic camshaft with a decompression device is known, for example, from the European patent application EP 0 407 699 A1.
Disadvantageous in all these known decompression devices is that the decompression function can generate stochastic clicking, which has an undesirable effect on the noise emission of the internal combustion engine. This clicking is caused by an unstable flyweight of the decompression device.
The object of the present invention is to prevent or at least reduce the acoustically conspicuous clicking of the decompression device.
This and other objects are achieved by a camshaft with a decompression device for an internal combustion engine, wherein in a base circle of a cam, which can be operationally connected with a gas exchange valve through rotation, a valve lifter is rotatably mounted, which is operationally connected with a rotatably mounted flyweight arranged coaxially to the camshaft in such a manner that the valve lifter from a certain rotational speed of the camshaft forms a contour of the base circle in the operational region with the gas exchange valve. The camshaft in the region of the flyweight has a cavity to which lubricant pressure can be applied and in the camshaft a radial first bore from the cavity to the flyweight is arranged, wherein in the first bore a slideable element that is displaceable by the lubricant pressure is arranged.
A slideable element installed in the camshaft is supplied with lubricant from the lubricating circuit. As soon as the internal combustion engine starts, this slideable element is radially shifted to the outside by centrifugal force. At the same time, the slideable element is supported by lubricant pressure and remains in the desired position and pushes the flyweight to the outside. In the process, the flyweight is held stable in the deflection position and, according to the invention, can no longer cause the clicking. Accordingly, the clicking is prevented through the configuration of the decompression function according to the invention and no unpleasant noises of the internal combustion engine are created.
With the configuration wherein lubricant can be applied to the cavity via a second bore from a bearing region of the camshaft it is ensured that adequate lubricant with adequate lubricant pressure is always available in order to push the slideable element in the direction of the flyweight.
The measure wherein the element is displaceable by the lubricant in the direction of the flyweight against a spring force of a spring element serves for the general stabilization of the decompression device.
The configurations wherein the flyweight comprises a stop for the element, and wherein the camshaft is a needle roller are preferred embodiments.
The configuration wherein the camshaft is an exhaust camshaft is a particularly preferred embodiment.
Preferentially, the camshaft according to the invention is installed in an internal combustion engine.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
In the following, the same reference numbers apply to identical components in the FIGS. 1 to 3.